The ear and the ear canal as a part of an organism are having individual acoustic qualities. The adaptation of hearing aids to these individual acoustic conditions is very complicated, takes great pain and is full of many uncertainties. After the insertion of a hearing aid or hearing device into the ear canal, a lot of different factors have important influence on the acoustic qualities, such as the remaining volume in the ear canal, the distance to the eardrum, the impedance of the eardrum, the transmission qualities of the inner ear, the fitting of the hearing aids, e.g. an otoplastique etc.
Acoustic impedance measuring are commonly carried out practically only for diagnostic purposes, known as Tympanometry, measuring of reflectance, measuring of compliance etc. Such diagnostic measurements will be carried out only at few frequencies, whereby varying the static pressure as a parameter in the ear canal. Most frequently the measurement will be carried out by a stimulation by means of a listener and the receiving of the stimulated sound by means of a microphone, which is coupled either directly or through adapters with the ear canal. The evaluation of this measurement is carried out via external, extensive electronics, most frequently with computer support, and the results are of interest only for diagnostic purposes. Due to this effort and the respective high costs, those proceedings are not suitable for use for the customization of hearing aids.
The measuring of the effective sound pressure in the ear canal takes a great effort and is frequently carried out by means of hose probes which are very sensitive with respect to its final position and even influences the sound system of the ear canal. Particularly measuring at higher frequencies are full of large uncertainties and error sources and therefore the results do not ensure any optimal customizations for the hearing aids.